Certain patterns of alcohol consumption shortly before conception and late in pregnancy are related to a woman's odds of giving birth to a full-term infant who is small for gestational age, according to an analysis of data from a multistate sample.1 Overall, women who binged on alcohol in the three months before pregnancy had slightly reduced odds of having an undersized infant (odds ratio, 0.9), but among women who drank moderately to heavily in a typical week, bingers had increased odds of this outcome (2.2); heavy drinkers had essentially the same risk as nondrinkers. In contrast, binge drinking in the last trimester of pregnancy was not associated with the likelihood that an infant was small for gestational age, but heavy alcohol consumption at this time was associated with sharply elevated odds (4.3).
To assess relationships between a woman's drinking habits and the risk that her infant will be small for gestational age, researchers retrospectively analyzed data from 19 states participating in the Pregnancy Risk Assessment Monitoring System for the years 1996-1999. Social and demographic information was obtained from infants' birth certificates and from questionnaires and telephone interviews completed within six months after birth. Women were asked how many drinks they consumed in an average week during the three months before they conceived and the last three months of pregnancy, and were classified as nondrinkers, light drinkers (three or fewer drinks per week), moderate drinkers (4-13 drinks) or heavy drinkers (14 or more drinks) for each period. Women were also asked if they binged on alcohol (consumed at least five drinks at one sitting) during each period.
Descriptive analyses were based on 50,461 women who gave birth to a live singleton infant at full term (37-42 weeks' gestation). Most of the women were white (79%), aged 18-34 (83%) and married (66%) and were not receiving public assistance (81%). More than three-fourths had at least a high school education. Nearly half had a normal weight before conceiving, and 82% did not smoke in late pregnancy.
Weighted data from the survey suggested that 44% of women in the study population drank during the three months before pregnancy and 6% during the last trimester, but almost all drank lightly. The proportions of women who binged on alcohol during the same periods were much smaller (13% and fewer than 1%), and about half of these women binged only once.
Sixteen percent of women gave birth to an infant who was small for gestational age (had a birth weight below the 10th percentile for gestational age). The proportion was significantly higher among women who drank heavily before pregnancy than among women who did not drink during this period (12% vs. 8%), but proportions among women who did and did not drink during the last trimester of pregnancy were similar, regardless of the level of drinking. Among women who drank heavily before pregnancy, a significantly larger proportion of those who had binged than of those who had not gave birth to an undersized infant (14% vs. 3%); similarly, among women who drank heavily in the last trimester, a significantly larger proportion of those who also binged than of others had an infant who was small for gestational age (36% vs. 0.4%).
Risk analyses were based on the 39,709 women for whom complete data were available. In a multivariate analysis that took into account maternal age and education, number of cigarettes smoked during the last trimester and other potentially risk-related factors, alcohol consumption before pregnancy, regardless of the level of consumption, was not associated with women's odds of giving birth to an infant who was small for gestational age. In contrast, heavy drinking during the last trimester of pregnancy was associated with a quadrupling of the odds (odds ratio, 4.3).
Among women overall, those who binged on alcohol before conceiving had a small but significant reduction in the odds of giving birth to an undersized infant relative to those who did not drink or who drank but did not binge (odds ratio, 0.9). However, among the subgroup of women who drank moderately or heavily before pregnancy, binge drinkers had odds that were twice as high as those of non-binge drinkers (2.2). Binge drinking in the last trimester of pregnancy was unrelated to the odds of having an undersized infant among women overall; its relationship to this outcome among moderate to heavy drinkers could not be assessed because few women reported both patterns of drinking at that time. For each time period, the number of binges had no association with the odds.
The researchers speculate that any protective effect of binge drinking near the time of conception may be due to vascular effects of alcohol that aid placental development or to differences in unmeasured dietary factors between drinkers and non- drinkers. "A well-designed prospective study examining the relations between nutrition, alcohol use, pre- pregnancy weight, pregnancy weight gain, and fetal growth would be valuable in determining what advice about diet and alcohol consumption is appropriate for women planning to become pregnant," the researchers conclude.
1. Whitehead N and Lipscomb L, Patterns of alcohol use before and during pregnancy and the risk of small-for-gestational-age birth, American Journal of Epidemiology, 2003, 158(7):654-662.